Methods will be developed to isolate opsonically active fibronectin from large volumes of human plasma. Good manufacturing practices and quality control standards for the production of parenterals will be adhered to. Methods for assay of its opsonic activity will be adapted to use with fresh, peritoneal, or cultured macrophages. The role of fibronectin in disease states will be explored. First, fibronectin will be measured in plasma from hospitalized patients to establish the extent of possible clinical need for this material. Second, the level of fibronectin will be measured in plasma from experimental animals suffering induced respiration distress. If found depleted, the effect of intravenous administration of human fibronectin will be determined.